Reference
Nominal dimensions for standard carbon-steel pipe to ASME B36.10M. The nominal pipe size (NPS) is a label, not a measured dimension — always size flow and pressure-drop calculations on the actual inside diameter, which depends on the schedule (wall thickness).
| NPS | OD (mm) | Sch 40 wall | Sch 40 ID | Sch 80 wall | Sch 80 ID |
|---|---|---|---|---|---|
| ½" | 21.34 | 2.77 | 15.8 | 3.73 | 13.88 |
| ¾" | 26.67 | 2.87 | 20.93 | 3.91 | 18.85 |
| 1" | 33.4 | 3.38 | 26.64 | 4.55 | 24.3 |
| 1½" | 48.26 | 3.68 | 40.9 | 5.08 | 38.1 |
| 2" | 60.33 | 3.91 | 52.5 | 5.54 | 49.25 |
| 3" | 88.9 | 5.49 | 77.93 | 7.62 | 73.66 |
| 4" | 114.3 | 6.02 | 102.26 | 8.56 | 97.18 |
| 6" | 168.28 | 7.11 | 154.05 | 10.97 | 146.33 |
| 8" | 219.08 | 8.18 | 202.72 | 12.7 | 193.68 |
| 10" | 273.05 | 9.27 | 254.51 | 15.09 | 242.87 |
| 12" | 323.85 | 9.53 | 304.8 | 17.48 | 288.9 |
Wall thickness and ID in mm. OD is fixed for a given NPS; a heavier schedule adds wall thickness inward, reducing the bore.
No. NPS is a dimensionless label. For ½" to 12" the outside diameter is fixed and larger than the number suggests, and the inside diameter depends on the wall thickness (schedule). Use the actual ID from this table in flow calculations.
A higher schedule number means a thicker wall for the same outside diameter, giving a higher pressure rating and a smaller bore. Schedule 40 is the common default; Schedule 80 is used for higher pressures or mechanical robustness.